\begin{tabular}{cccc}
    \toprule
    & \multirow{2}{*}{\shortstack{Compliance Period}} & \multicolumn{2}{c}{Data Collection} \\ \cmidrule{3-4}
    & & Survey & CEMS \\ \midrule
    \gray Dec-2018 & \gray  & \blue & \\
    \gray & \gray  & \blue & \\
    \gray & \gray & \blue & \\
    \gray & \gray  & \blue \multirow{-4}{*}{\shortstack{Baseline survey}} \\
    Apr-2019 & & & \blue  \\
    % & & & \blue \\
    & & & \blue \multirow{-2}{*}{\shortstack{CEMS data \\ begins}} \\
    \gray Jul-2019 & \gray Mock-I & & \blue \\
    Aug-2019 & Mock-II & & \blue \\
    \gray Sep-2019 & \gray Period-I & & \blue \\
    Oct-2019 & Period-II & & \blue \\
    \gray Nov-2019 & \gray Period-III & & \blue \\
    Jan-2020 & Period-IV & & \blue \\
    \gray Feb-2020 & \gray Period-V & & \blue \\
    Mar-2020 & Period-VI & & \blue \\
    \gray Apr-2020 & \gray & & \blue \\
    \gray & \gray & & \blue \\
    \gray & \gray & & \blue \\
    \gray & \gray & & \blue \\
    %\gray & \gray & & \blue \\
    \gray & \gray \multirow{-5}{*}{\shortstack{Interregnum \\ \textit{(COVID-19)}}} & \blue & \blue \\
    Oct-2020 & Mock-III & \blue & \blue \\
    \gray Nov-2020 & \gray Interregnum \textit{(Diwali)} & \blue  & \blue \\
    Dec-2020 & Period-VII & \blue  & \blue \\
    \gray Jan-2021 & \gray Period-VIII & \blue \multirow{-5}{*}{\shortstack{Endline survey}} & \blue \\
    Feb-2021 & Period-IX & & \blue \\
    \gray Mar-2021 & \gray Period-X & & \blue \\ 
    \bottomrule
\end{tabular}